Yes, the colors/background of the skin can change or not, depending on whether there are prefabricated.
Of course, you also can modify (or make a new) skin file to make it meet your needs.
Reference:
- How can I create new skins? (www.rainlendar.net/cms/index.php?option=com_easyfaq&Itemid=26#faq6)
- The "Skinning Tutorial" in Rainlendar2's Help-File. (Right-Click > Help)